1. Field of the Invention
The present invention is related to a temperature-dependent switch having two connection electrodes mounted on an insulating support, a switching mechanism that as a function of its temperature makes an electrically conductive connection between the two connection electrodes, and a resistance element that is connected to the two connection electrodes electrically parallel to the switching mechanism.
2. Related Prior Art
A switch of this kind is known from DE 21 13 388 A.
The known switch is a thermostat for protecting an electrical device, the switch being connected electrically in series with the device to be protected and in thermal contact with the device.
The two connection electrodes are planar metal parts of which one carries a fixed countercontact and the other a bimetallic element on whose free end sits a movable countercontact coacting with the fixed countercontact. The two metal parts are arranged one above another, and clamp between them a PTC resistor that, with interposition of a spring, is in electrical contact with both connection electrodes.
This configuration made up of insulating support, metal parts with fixed and movable countercontacts, and PTC resistor is slid into a housing, whereupon the housing opening is encapsulated with a sealing compound.
If the temperature of the device being protected exceeds the response value of the bimetallic element, the latter lifts the movable countercontact away from the fixed countercontact, thereby interrupting the supply of current to the device. A small residual current now flows through the PTC resistor arranged parallel to the switching mechanism thus constituted, developing sufficient heat to hold the switching mechanism open; this function is called "self-holding."
A disadvantage with the known switch is that the PTC resistor is mechanically retained only when the switch is completely assembled, making assembly of this switch quite complex. Replacement of the PTC resistor is not possible.
A further self-holding temperature-dependent switch is known from DE 43 36 564 A1. This known switch comprises a bimetallic switching mechanism arranged in an encapsulated housing. The housing is arranged on a support plate on which conductor paths and resistors are provided. A PTC resistor, which is soldered parallel to the switching mechanism with external connectors, is provided outside the housing on the support.
A disadvantage of this switch is that it not only requires a relatively large number of components, but also has large dimensions.